A liquid crystal display device is provided with a liquid crystal driver for driving a liquid crystal panel for example. The liquid crystal driver generates a liquid crystal driving output, that drives the liquid crystal panel, from a liquid crystal driving voltage. As to the liquid crystal driver, the following conventional techniques are mainly applied, so as to obtain the liquid crystal driving voltage, according to purpose of use of the liquid crystal panel.    1. A technique in which liquid crystal driving voltages are provided to all the plurality of liquid crystal drivers from an external power source provided as a part of the liquid crystal driver.    2. A technique in which a voltage which functions also as a logic voltage is provided to the liquid crystal driver from a power source for logic driving so as to generate the liquid crystal driving voltage in the liquid crystal driver (note that, in a case where a voltage is generated by boosting the logic voltage, each liquid crystal driver includes a boosting circuit therein).    3. A technique in which a voltage which functions also as the logic voltage is provided to one of plural liquid crystal drivers, so as to generate the liquid crystal driving voltage in the liquid crystal driver, then providing the liquid crystal driving voltage to other liquid crystal drivers (note that, in a case where the liquid crystal driving voltage is generated by boosting the logic voltage, the corresponding liquid crystal driver includes a boosting circuit therein).
FIG. 7 shows an example of the foregoing prior art 1. A display device drive unit 101 shown in FIG. 7 is provided with a plurality of, for example, four liquid crystal drivers 103. A logic voltage of 3V for example and a liquid crystal driving voltage b of 15V for example are inputted from an external power source (not shown) to the liquid crystal drivers 103. Besides, a control signal c and a data signal d are inputted from a controller (not shown) to the liquid crystal drivers 103. Note that, description concerning a driver for driving a common electrode is omitted. The description is also omitted in FIG. 8 illustrating the prior art 2 and FIG. 9 illustrating the prior art 3.
In each liquid crystal driver 103, a liquid crystal driving output e of 0 to 15V for example is generated from the liquid crystal driving voltage b in accordance with resistance division etc. for example. The liquid crystal driving output e is outputted to the liquid crystal panel 102 in accordance with the control signal c and the data signal d. Thus, display is created in the liquid crystal panel 102 in accordance with the data signal d.
In the arrangement of the prior art 1, the liquid crystal driving voltage b is provided from the external power source, so that an extra circuit such as the boosting circuit is not required in the liquid crystal driver 103.
Next, FIG. 8 shows an example of the prior art 2. A display device drive unit 111 shown in FIG. 8 includes two liquid crystal drivers 112, and each of the liquid crystal drivers 112 has a boosting circuit 113 and a driving circuit 114. The logic voltage a of 3V for example is provided from a logic driving power source (not shown), which functions as an external power source, to each boosting circuit 113. Further, the control signal c and the data signal d are inputted from a controller 115 to the liquid crystal driver 112.
The boosting circuit 113 of the liquid crystal driver 112 generates the liquid crystal driving voltage b of 15V for example by boosting the logic voltage a of 3V for example, and the liquid crystal driving voltage b is outputted to a driving circuit 114. In the driving circuit 114, a liquid crystal driving output e of 0 to 15V for example is generated from the liquid crystal driving voltage b, and the liquid crystal driving output e is provided to the liquid crystal panel 102 in accordance with the control signal c and the data signal d.
In the display device driving unit 111, a dual scan mode based on a duty driving system using an STN liquid crystal is applied. In this case, a segment electrode of the liquid crystal panel 102 is divided into two electrodes (upper and lower electrodes), and there are provided the liquid crystal drivers 112 which drive the upper and lower electrodes respectively.
Next, FIG. 9 shows an example of the prior art 3. A display device driving unit 121 shown in FIG. 9 includes two liquid crystal drivers 122a and 122b, and each of the liquid crystal drivers 122a and 122b includes the boosting circuit 113 and the driving circuit 114. The logic voltage a of 3V for example is provided from the logic driving power source (not shown), that functions as an external power source, to each boosting circuit 113. Further, the control signal c and the data signal d are inputted from the controller 115 to the liquid crystal drivers 122a and 122b. 
Each of the liquid crystal drivers 122a and 122b includes a setting terminal 123, and how voltages are provided to the liquid crystal drivers 122a and 122b varies depending on how the setting terminal 123 is set.
That is, the liquid crystal driver 122a, in which the setting terminal 123 is set to be High (logic power source voltage), allows the boosting circuit 113 to function. Thus, the logic voltage (3V) a is inputted to the liquid crystal driver 122a, so that the liquid crystal driving voltage (15V) b obtained by boosting the logic voltage a can be externally outputted.
While, the liquid crystal driver 122b, in which the setting terminal 123 is set to be Low (GND potential), does not allow the boosting circuit 113 to function. Thus, the liquid crystal driving voltage b is inputted from the outside to the liquid crystal driver 122b. Namely, the liquid crystal driving voltage b is inputted from the boosting circuit 113 of the liquid crystal driver 122a via a power feeder 124. The setting of the liquid crystal driver 122a is called “master mode”, and the setting of the liquid crystal driver 122b is called “slave mode”.
As described above, the liquid crystal driver 122a in the master mode generates the liquid crystal driving voltage b from the logic voltage a by means of the boosting circuit 113, and generates the liquid crystal driving output e from the liquid crystal driving voltage b by means of the driving circuit 114, so as to cause the liquid crystal panel 102 to create display in accordance with the liquid crystal driving output e. Further, the liquid crystal driving voltage b is outputted to the other liquid crystal driver 122b. 
While, the liquid crystal driver 122b receives the liquid crystal driving voltage b from the liquid crystal driver 122a in the master mode, and generates the liquid crystal driving output e from the liquid crystal driving voltage b by means of the driving circuit 114, so as to cause the liquid crystal panel 102 to create display in accordance with the liquid crystal driving output e.
Note that, Japanese Unexamined Patent Publication No. 62746/1998 (Tokukaihei 10-62746)(Publication date: Mar. 6, 1998) discloses a similar technique, but it does not concern a power source. That is, this publication indicates a mode such that: a level shifter, which level-shifts an input signal of a vertical driver (corresponding to a common electrode driver) operating at a high voltage, is disposed only on a vertical driver in a master mode, and the input signal, outputted from the vertical driver in the master mode, that has been level-shifted, is received by a vertical driver in a slave mode.
It is general that the liquid crystal panel driven by the liquid crystal driver is under a loading condition in terms of capacity, so that it is necessary to charge and discharge the liquid crystal panel. Thus, a power source of the liquid crystal panel is required to provide a large quantity of current according to variation of outputs. In a case where power supplying ability is insufficient, a power source voltage itself varies. As a result, a bad influence is exerted on display of the liquid crystal panel.
The prior art 1 has the following advantage: external power sources providing the liquid crystal driving voltages b are additionally provided on all the plurality of liquid crystal drivers 103, so that it is possible to provide a power source appropriate for a property of the liquid crystal panel 102.
However, it is necessary to provide the external power sources. This increases the cost, and brings about necessity to make rooms for packaging the power sources thereon.
The prior art 2 is such that: the respective liquid crystal drivers 112 include the boosting circuits 113 which function as the power sources, so that the boosting circuits 113 are dispersively provided on the respective liquid crystal drivers 112. Thus, the power supplying ability of the boosting circuit 113 may be a little. Further, this does not increase the cost unlike the case where additional power sources are packaged.
However, it is impossible to equalize output voltages of the individual boosting circuits 113, that is, the output voltages are different from each other. Thus, it is difficult to create high quality display in the liquid crystal panel 102. That is, although preferable results may be brought about by other display conditions and display properties, the following problem tends to be brought about: as to the liquid crystal panel 102, in a case where one liquid crystal driving voltage b is different from other liquid crystal driving voltage b by 10 mV when a uniformed image is displayed on the entire screen for example, human eyes recognize the difference. Thus, it is impossible to use the prior art 2 in the case where the uniformed image is displayed on the entire screen. Further, it is general that power consumption of the boosting circuit 113 is large. Thus, when the boosting circuit 113 is operated in the liquid crystal driver 112, the power consumption of the liquid crystal driver 112 is increased.
The prior art 3 is such that: the boosting circuit 113 which functions as the power source is operated in a single liquid crystal driver 112, and the liquid crystal driving voltage b obtained therefrom is provided to other liquid crystal driver 122b. Thus, it is possible to reduce the power consumption. Further, variation of the output voltage of the boosting circuit 113, that is, variation of the liquid crystal driving voltage b uniformly occurs in each of the liquid crystal drivers 122a and 122b. Thus, this brings about an advantage that uneven display brought about by the variation of the liquid crystal driving voltage b is hardly seen.
Particularly in a case where a liquid crystal panel for a cellular phone is operated in accordance with dual scan driving, the following arrangement is applied: The liquid crystal drivers are disposed along both ends (upper and lower ends in FIG. 9) of the liquid crystal panel 102 as shown in FIG. 9, and the one is used in the master mode to obtain the liquid crystal driving voltage b by boosting, and the other is used in the slave mode to receive the liquid crystal driving voltage b that has been generated in the master mode. In this case, there is an advantage that: it is possible to simplify the power source circuits in the entire system, and to reduce the number of the boosting circuits 113 which consume a large quantity of current, and to uniform the liquid crystal driving voltages b in the respective liquid crystal drivers.
Incidentally, the invention of the aforementioned Tokukaihei 10-62746 includes LSIs which are different from each other as a master chip and a slave ship, that is, an LSI having the boosting circuit 113 therein and an LSI having no boosting circuit 113 therein. In this case, it is necessary to form LSIs, different from each other in a circuit arrangement, that function as the liquid crystal drivers, so that this increases the cost. Then, there is provided the setting terminal 123, which is used to switch between the master mode and the slave mode as shown in FIG. 9, so that there is formed an LSI which can be switched between the master mode and the slave mode. Upon packaging the LSI on the liquid crystal panel 102, the setting terminal 123 is set (fixed) to a desired mode.
However, according to the arrangement in which the liquid crystal driver is set to be in the desired mode by means of the setting terminal 123, it is necessary to provide a signal wiring 125, setting the mode, that is connected to the setting terminal 123 upon packaging the liquid crystal driver (LSI). Alternately, in a plurality of packages of the liquid crystal driver (LSI), for example, in TCPs (tape carrier packages), it is necessary to prepare a setting terminal whose level is fixed to High level and a setting terminal whose level is fixed to low level in the wiring provided in the TCP. Thus, this increases the cost.
Further, in the foregoing arrangement, it is impossible to switch the power supplying mode (current supplying ability) once the liquid crystal driver (LSI) is packaged. Thus, in the case where the ability of the power source is insufficient corresponding to the display condition, it is impossible to switch the voltage supplying mode so as to exhibit the ability required in creating display. As a result, it is necessary to set the power source by estimating the maximum power consumption, so that this increases the cost.